Well, that's exactly where my question comes from. Since I work in the customer SAP support team all I really care for is whether we can deliver the interfaces our users need "by hook" (API) or "by crook" (BDC).
So far SAP have not delivered the APIs for the whole spectrum of their functionality. There are BAPIs that cover large parts of it (but not all), then every few years comes "yet another framework" that usually does not deliver much content and fizzles. Yet BDC is like the cockroach of the SAP world - it'll survive even HANA. 